The invention relates to a magnetic head which includes a magnetic core having a gap-forming area, and a layer of non-magnetizable bonding material in the gap-forming area of the magnetic core. The head also includes diffusion barriers provided between the core parts and the layer of non-magnetizable material. The invention also relates to a method of manufacturing such a magnetic head.
Magnetic heads serve to record, playback and/or erase magnetic information. They are used, for example, in tape recorders for recording and/or playing back audio information or video information. Particularly when a magnetic head is used in tape recorders for recording and/or playing back video information (so-called video recorders), it is usual to manufacture the core of the magnetic head from (monocrystalline) ferrite.
The gap of a magnetic head for a video recorder is formed by bonding two parts of (monocrystalline) ferrite to each other by means of a sputtered film of a low-meltingpoint glass. In order to prevent the glass from attacking the ferrite during bonding at approximately 700.degree. C., the ferrite is first coated with a layer which is impervious to glass and which is often termed a diffusion barrier. Although British Patent Specification No. 1,317,634 suggests as materials for the diffusion barrier: non-magnetizable metals, metal oxides, borides, nitrides, silicon oxide and ferrite which is non-magnetizable at room temperature, a sputtered SiO.sub.2 layer has so far been used in practice as the diffusion barrier. In the heating phase of the bonding process, the glass becomes less and less viscous. When the glass is heated to a sufficiently high temperature it may work as an adhesive. However, above a given temperature, the SiO.sub.2 -layer dissolves in the glass. As a result, the glass becomes more viscous so that its value as an adhesive decreases. In the manufacture of heads, heating to 700.+-.5.degree. C. has to be done quickly (in approximately 10 minutes) so as to obtain a good bonding. It has been found difficult to maintain this narrow tolerance of .+-.5.degree. C.
So the search is for a diffusion barrier which permits a freer temperature adjustment. It was expected that silicon nitride, which is known from I.C. technology to be impervious to glass in certain circumstances, might be suitable. A glass-bonded ferrite head with a silicon nitride barrier has been suggested in German Offenlegungsschrift No. 2,341,649.
It has been found, however, that thin Si.sub.3 N.sub.4 layers having ferrite as a substratum are damaged after termination of the temperature cycle of the bonding process. The glass penetrates through the chinks formed, flows below the Si.sub.3 N.sub.4 and attacks the ferrite.
The damage to the Si.sub.3 N.sub.4 layer is probably the result of the high elastic stress at the interface Si.sub.3 N.sub.4 -ferrite. This stress may substantially be ascribed to the comparatively low elasticity of Si.sub.3 N.sub.4.